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Misc. UL and Bias Questions

7/21/2000 3:26 AM
morris
Misc. UL and Bias Questions
I'm just getting my homebrew amp up and running and I had some questions.  
 
1. I've got a pair of 6v6's connected in UL. I'm using 470-ohm screen grid resistors. My plate voltage is 378V while my screen voltage is 380V. Is this normal for UL connections? I'm drawing around 2-3 milliamps of screen current per tube at idle; is that about right?  
 
2. The amp is cathode-biased, currently with a 330-ohm resistor bypassed with a 50 uf cap. I'm getting around 27V at the cathodes. When calculating plate dissapation should I multiply the plate current by the plate-to-ground voltage or the plate-to-cathode voltage?  
 
3. I've heard that the current in an UL amp doesn't change as much from idle as a straight pentode amp. Is this true, and if so, approximately where should I bias this amp compared to the 14W max dissapation for 6v6's (which I believe I'm very close to right now)?  
 
One more thing; my heater voltages are running high even with all the tubes installed. 7.1V for the 6.3V heaters and 5.6V for the 5V heaters. How big of a problem will this be?  
 
Thanks in advance for all of your help!  
 
Morris  

 
Replies:
Ken Gilbert hey morris.brian's ... -- 7/21/2000 10:38 PM